[m463]

Safest roads have the speed limit 5-10 mph below the road design speed.

see fig 4 on speed variance:

https://www.fhwa.dot.gov/publications/research/safety/17098/...

going faster or slower than average traffic speed shows markedly greater accident rate.

note that this can apply not only to speed limits, but things like express lanes going different speeds than other lanes

[durkie]

But you're saying the speed limit (being too high or low) makes the road dangerous. Aren't the people driving their cars too fast making the road dangerous?

[Leif24]

A great many people when they see a open straight road with little obstacles or pedestrians will go 45-50 MPH. A great many people when they see a 15 MPH sign will go 20 MPH. Pair that low speed limit with a "fast" road and you will end with many people going 45 MPH and many people going 20 MPH. This variance in speed, with some people going much slower than others can be more dangerous than if most went the same speed - e.g. if the limit were 45 MPH.

You are correct that people driving too fast make the road dangerous, but so does people driving too slow. Generally, from a safety point of view, you want the slowest speed at which almost everyone will actually drive at, as large variance in speed between drivers is dangerous. I think this is what the parent post was getting at: a speed limit too fast OR too slow will increase the number of accidents, keeping in mind that there will always be at least some drivers speeding.

[david-gpu]

> You are correct that people driving too fast make the road dangerous, but so does people driving too slow.

It's accurate to say that people driving too fast are extra dangerous when there are slower vehicles in the road. The danger is still caused by the people driving too fast, not by those driving slowly, though. Speed kills.